1. Field of the Invention
The present invention relates to a headlight device for a vehicle such as an automobile and the like and, particularly to a novel headlight device adapted for that having a reflector with the optical axis thereof being inclined relative to the optical axis of the headlight.
2. Description of Prior Art (FIGS. 7 and 8)
Various headlights have been proposed and utilized, and it is usually required that a desired pattern is formed by the light beam of the headlight so as to improve the safety in the traffic.
FIG. 7 is a schematic perspective view of an automotive headlight "a" according to prior art, in which x-axis is an axis passing the first focus "f" of the reflective surface "c" of a reflector "b" of the headlight "a" and the focus "e" of a projector lens "d" which is disposed in front of the reflector "b", and y and z-axes are determined to intersect orthogonally with each other and with the x-axis at the apex of the reflector "b".
The reflective surface "c" is formed to converge the light emitted from a light source "g" being located on the first focus "f" of the reflective surface "c" into the pattern of a quadratic curve "h" (which is referred hereinafter as a focal line) as viewed in the plan view.
Shown at "i" is a shade plate being disposed between the reflector "b" and the projector lens "d" and has a light cutting edge "j" on the upper edge thereof to define the upper edge of the light distribution pattern. The light cutting edge "j" has nearly the same configuration with the focal line "h" (a part of an ellipse in the drawing) as viewed in the plan view, and the edge "j" is located near to the focal line "h" of the reflector "b". The focus "e" of the projector lens "d" is located on the center of the light cutting edge "j" of the shade plate "i".
In the headlight "a", the light "k", "k", . . . emitted from the light source "g" being located on the first focus "f" of the reflective surface "c" of the reflector "b" and reflected by the reflective surface "c" will converge on the focal line "h" and, since the configuration of the focal line "h" is nearly the same to that of the light cutting edge "j" of the shade plate "i", a portion of the reflected light is shaded by the cutting edge "j" to form the light distributing pattern "l" as shown in double dotted chain line in FIG. 8(B) which has distinct upper edge as shown in the drawing. Incidentally, line H--H in the drawing is the horizontal line and line V--V is the vertical line.
However, when the reflector "b" is applied to such as a headlight a' which is shown in FIG. 8(A) and described in U.S. patent application Ser. No. 250,881, now U.S. Pat. No. 4,851,968, there arises following problems.
In the headlight a', the reflector is divided into a main reflector b'.sub.m positioned on the lower half with respect to the optical axis X--X for forming the high beam, and a sub reflector b'.sub.s positioned on the upper half of the reflector for forming the low beam. The optical axis of the main reflector b'.sub.m is the axis X.sub.m --X.sub.m which inclines lower and forward relative to the axis X--X, and the optical axis of the sub reflector b'.sub.s is the axis X.sub.s --X.sub.s which inclines upper and forward relative to the axis X--X. The electric bulb is formed to have a main filament m' nearly on the first focus f'.sub.1 of the main reflector b'.sub.m and a sub filament n' nearly on the first focus f'.sub.2 of the sub reflector b'.sub.s.
Thus, when aforementioned reflective surface "c" of the reflector "b" is used as the reflective surface c'.sub.s of the sub reflector b'.sub.s the light emitted from the sub filament n' and reflected by the reflective surface "c" (shown as light k', k', . . . ) will converge on the focal line h' within a plane which is parallel to a plane including the optical axis X.sub.s --X.sub.s of the sub reflector b'.sub.s and is projected forward through the projecting lens d' but, a portion of the reflected light is shaded or cut off by the light cutting edge j' of the shade plate i'. The light beam makes the pattern "o" as shown in the solid line in FIG. 8(B). The pattern "o" has drooped opposite end portions o' and o' as shown in the drawing. Therefore, desired pattern cannot be obtained.
Specifically, as shown in FIGS. 9(A) through 9(C), when a transparent plate "q" having a figure "p" representing the focal line thereon is rotated as shown in arrow line in FIG. 9(A) and is viewed from the arrow B direction, then, the opposite ends of the figure "p" which were initially seen on a straight line will increasingly displace upward as shown in FIG. 9(B). The projector lens d' acts to form the inverted image as shown in FIG. 9(C) which has the drooped opposite ends.